This invention relates to a brake rotor constructed from a hat-shaped carrier and at least one friction ring located on or on top of the carrier.
Similar brake rotors are known as components of braking systems, especially for use in motor vehicles. Known brake rotors are made of cast gray iron and comprise a hat-shaped carrier section and a friction ring arranged at the circumference of the carrier section.
Known cast gray iron brake rotors have a coefficient of thermal expansion of 10.sup.-5 K.sup.-1. They exhibit, at increased temperatures resulting from the application of the brake pads, a radial expansion and also an axial expansion due to the connection of the friction ring with the hat-shaped carrier section (commonly known as umbrella distortion). To minimize undesirable umbrella distortion, known brake rotors employ grooves to block heat transfer.
It is known that to accomplish higher temperature capability, friction rings used in motor sport applications are constructed of carbon/carbon and/or ceramic materials. Drilled holes increase the ventilation of the brake rotor.
The attachment of the friction ring to the hat-shaped brake rotor requires a variety of fastener hardware such as bolts, spacer bushings, nuts, washers etc. This attachment of the friction ring to the brake rotor transmits torque and accommodates the thermal expansion of the different component materials. Because of new carbon/carbon and ceramic friction materials, the brake rotor and fastener components must withstand higher temperatures. The disadvantages of attaching the friction ring to the brake rotor in this manner include a high part number count, the additional assembly work required, and the potentially negative effect on comfort. Required manufacturing tolerances regarding parallelism, thickness and runout have a negative effect regarding comfort even with the known cast gray iron brake rotors.
One object of this invention is to provide a brake rotor which overcomes the disadvantages of brake rotors manufactured per the current state of technology as described above. Another object is to provide a brake rotor that is easy to manufacture and install. In addition, an object is to provide a brake rotor able to operate at higher temperatures without exposing nearby components of the wheel, especially the wheel bearing and rim, to higher temperatures. Moreover, another object of the brake rotor is low cost and preferably low weight.
These and other objects are obtained by the present invention. The brake rotor of the present invention includes a friction ring made of a high performance friction material from the group of fiber reinforced ceramic materials, and a carrier made of a material from the group of carbon/carbon materials; the coefficients of thermal expansion for these materials are at least approximately the same; and the friction ring and carrier are immovably attached to each other. By using the same or similar materials having a low thermal expansion, the occurrence of the previously described umbrella distortion is eliminated. In addition, because of the low thermal conductivity of the carrier material, only a small portion of the heat generated by the braking process is conducted to the wheel bearing and rim of the wheel being braked.
The brake rotor of the present invention is easier to manufacture and assemble than known brake rotors from motor sport, which use a floating assembly, because there are fewer parts to handle. Additionally, the brake rotor of the present invention provides improvements in comfort because tolerance buildup, experienced with known brake rotors due to the assembly of the friction ring to the brake rotor, does not occur with the present invention.
A particularly advantageous configuration of the brake rotor of the present invention is the arrangement of friction rings on both sides of the flanged outside diameter portion of the hat-shaped carrier.
The brake rotor further includes attachment of the friction ring(s) to the carrier by riveting, bonding or a homogeneous material joint.
The brake rotor includes a carrier configuration with recesses on its flange portion for ventilation which cover the radial dimensions of the friction rings attached on both sides and provides cooling to the 5 friction rings. Recesses serve as cooling channels and do not require subsequent drilling or elaborate assembly of brake rotor halves to form cooling channels, as required with known brake rotor configurations. The recesses are readily produced as an integral step in the manufacturing 10 process.
Another aspect of the invention is that the hat-shaped carrier contains a flanged bottom in the center of the part to facilitate a bolted attachment to the wheel flange. Attachment to the wheel flange with bolts is preferred to further reduce the number of required parts for assembly.
The objects of the present invention may be obtained by employing a manufacturing process characterized such that the carrier and the friction ring are molded separately into pre-forms. They are subsequently joined together and finish-formed in a press tool. Accordingly, the carrier and friction rings are separately pre-formed in a molding press and subsequently assembled and finish molded into a single part. The process is proven, very efficient, and highly accurate.
This method of manufacture is especially advantageous where an additional process after the molding process is employed to convert the molded part into carbon/carbon material. Through this process the material transition joint present after molding between friction rings and carrier is eliminated. The result is a seamless material transition--the brake rotor becomes, in effect, a single piece part. This leads to especially homogeneous thermal conductivity as well as very good stability of the brake rotor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.